Here's what I've found:
There's a pg.c, starting in System Vr2. R1 didn't have it.
It changed in a number of fussy ways, but nothing substantial.
It grew that copyright notice in SVr3, but the sun one quoted is missing
/* Copyright (c) 1990, 1991 UNIX System Laboratories, Inc. */
that should have been there to, suggesting it was snagged between r2 and r3.
There's also two other copies of pg as well. There's one in 32V. Though a quick diff suggests little in common with the System Vr2 version.
There's also one in the BRL/JHU pdp-11 version of unix that is nearly identical to the System Vr2 one. Though it's dated 1985 while the SVr2 one is 1983. Both with a 1984 copyright by AT&T.
SunOS 4.1.3 shipped with the System Vr2 version. in 5bin.
Irix 6.5.5 had what looks like the System Vr3 copy in it, though I didn't delve into it.
So this supports the recollections here that it was from System Vr2...
However, there's also a Doug Gwen version from the Delaware 1980 Usenix tape submitted by geotronics and on other tapes. Haven't delved on what makes these different from each other though.
There's one in the NOSC unix we have in the archive, unrelated, it seems to either of these. It's dated in 1979.
There's still another one on the UNSW tapes from 1978 by Sape Mullender Informatics staff Vrije Universiteit Amsterdam. Also independent. It's on the 4th tape we have in the archive.
10th edition also has pg.c, but it's an I/O pager for the kernel.
Which explains another comment in the System Vr2 one:
* Note: The reason that there are so many commands to do
* the same types of things is to try to accommodate
* users of other paginators.
Warner